After downloading and installing the ECW SDK it is necessary to copy the runtime DLLs from the redistributable\vc90\win32\ directory to somewhere appropriate, like C:\Windows\system32 (32-bit Windows), C:\Windows\SysWOW64 (64-bit Windows), or C:\OSGeo4w\bin.

Note that downloading and installing these DLLs requires agreeing to a license. Please review the license terms carefully.

It is imperative that the VC9 ECW 4.2 SDK binaries be used. Any other ECW (NCS*) DLLs are unlikely to work properly. However, it's reported that 4.1 SDK ECW DLLs seem to work as well.

Failure to install the correct ECW libraries will normally result in a popup message reading "This application has failed to start because NCSEcw4_RO.dll was not found." or a console error report like: